Current methods for assessing improvement in movement disorders in clinical trials and clinical practice are insensitive, qualitative, offer limited reliability and repeatability, and require a large number of subjects. Many patients have gait and balance resulting in high fall risk, but clinicians have no practical method to objectively measure these responses for either clinical trials or clinical practice. Postural transitions such as rising from a chair and turning are particularly difficult for people with movement disorders such as Parkinson's disease or the frail elderly. The most commonly used test of fall risk from problems with postural transitions and slow gait is the Get Up and Go test (clinical TUG).
The Timed Up and Go test (TUG) is a widely used clinical test to evaluate balance and mobility. The TUG test uses a stop-watch to time how long it takes a subject to stand up from a chair, walk 3 meters, turn 180 degrees, walk back to the chair and sit down. The TUG test has been shown to predict falls in the elderly, reflect balance deficits and correlate with severity of moderate-to-severe Parkinson's disease. The clinical utility of the TUG is probably due to sequencing several mobility skills, such as turning and sit to stand transitions that require balance control, as well as straight-ahead gait.
The traditional TUG is limited, however, because performance is rated only by a single, total duration score from a stop-watch, so that it is not possible to determine which balance or gait subcomponent of performance are affected. Recently, researches have used a stop-watch to measure the duration of each of the four subcomponents of the TUG, namely sit-to-stand, gait, turning and turn-to-sit. However, using a stop-watch to find exact time of a rapid sequence of activities is difficult. To address this issue, a recent study used inertial sensors to measure the duration of each subcomponent of the TUG test automatically.
An important step needed to build a complete system to analyze all subcomponents of the TUG test is to analyze 180° turns. A difficulty in analyzing turning is defining the onset and offset of turns. Researchers have used angular velocity in the yaw-axis and a fixed threshold to define onset and offset of turning. A problem with fixed thresholds is that their exact value is hard to justify, may be dependent on the population, and tends to be influenced by noise and movement artifacts.
Besides providing detailed assessment of subjects' performance, a useful movement analysis system should be reliable. The TUG, itself, is a reliable test and a recent study has shown good test-retest reliability for the duration of its subcomponents. A useful clinical assessment tool also needs to be sensitive to pathology. While it is known that patients with advanced stages of Parkinson's disease (PD) show impaired motor performance compared to control subjects, it is difficult to identify mobility deficits in very early stages of their disease.